Note: E2B requires MBR ptn #4 to be unused (and ptn #3 should be free too, if you want some other features like linux booting with persistence).Check partitions using RMPrepUSB.exe - Drive Info - 0.
If possible, use FAT32 or NTFS for the 1st partition and ensure it is large enough (16GB-128GB). I recommend you avoid Logical partitions if you have a Removable USB drive.
Recommended for Easy2Boot (fastest flash drive!)
SanDisk Extreme SDCZ880-128G-G46
Fastest USB 3!
See Blog post